Path: Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail
NNTP-Posting-Date: Wed, 10 Apr 2024 15:46:54 +0000
From: John Larkin <jjSNIPlarkin@highNONOlandtechnology.com>
Newsgroups: sci.electronics.design
Subject: Re: Inductance meter for BIST
Date: Wed, 10 Apr 2024 08:45:09 -0700
Organization: Highland Tech
Reply-To: xx@yy.com
Message-ID: <27cd1jhkj6f02vmlpgk4tlc1t5d0ojeban@4ax.com>
References: <go191jli8laisgsbhrrp3fmn113fi5p578@4ax.com> <jnia1j1t40g4ldpk5tkbj6ori2ej13d9ls@4ax.com> <uv3na4$a5pd$1@dont-email.me> <qkta1j1d6rssgifim5vldca5c72ofcgstc@4ax.com> <uv4411$dd73$1@dont-email.me>
X-Newsreader: Forte Agent 3.1/32.783
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Lines: 80
X-Trace: sv3-p9QuDiRkvnWNzMDFPMSKMmwYQCcjnUINMRIbb21TbsNKQn/2jZITW+8HA6jrNURzgr4/f0c4LnAhEqW!NVNEEX+Ij9UIifjzXLR6FJ9L33XjgbLdzwDPv5QprktWQkuUyH7LgxC+Bs+7JaH9w0ZVk1yoV9u/!fgdraA==
X-Complaints-To: www.supernews.com/docs/abuse.html
X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly
X-Postfilter: 1.3.40
Bytes: 4414

On Tue, 9 Apr 2024 21:13:30 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:

>On 4/9/24 19:17, john larkin wrote:
>> On Tue, 9 Apr 2024 17:36:28 +0200, Jeroen Belleman
>> <jeroen@nospam.please> wrote:
>> 
>>> On 4/9/24 16:19, John Larkin wrote:
>>>> On Mon, 08 Apr 2024 17:17:15 -0700, john larkin <jl@650pot.com> wrote:
>>>>
>>>>> I can build this into my new programmable inductor module, for
>>>>> self-test. With a 1% cap, it should be plenty good. L range will be
>>>>> 750 mH down to maybe 10 mH, part of simulating solenoids and torque
>>>>> motors and such.
>>>>>
>>>>> If I add a switch to open R3 and run some current through R1, it can
>>>>> measure series resistance too.
>>>>>
>>>>> https://www.dropbox.com/scl/fi/tn8lpk38677ioylhdkget/P955_L-meter.jpg?rlkey=xynqyzfc2x020llr3a945c0td&raw=1
>>>>>
>>>>> https://www.dropbox.com/scl/fi/gojlqxj23r4m57ke9jhui/Ind_Meter_1.asc?rlkey=if40kmtiz49gp62bacfvju3uv&dl=0
>>>>
>>>> Most L-meters, the AADE sort, lie or don't work with big Ls.
>>>>
>>>> This is better:
>>>>
>>>> https://www.dropbox.com/scl/fi/9tex1slpnaqz4n2cbxp3n/Ind_Meter_Apr_9.jpg?rlkey=52vbyylc5ax48w54qdxm9r9cq&raw=1
>>>>
>>>> Given a small uP, like the Rasp Pi thing, it could measure L and Rl
>>>> pretty easily. One could get compusive and math out the small
>>>> inductance measuring error from the inductor copper resistance.
>>>>
>>>> I need repeatability more than accuracy, and don't have time to
>>>> explore this very deep, but it's interesting.
>>>>
>>>> I've been buying shaftless torque motors off ebay, to understand them
>>>> electrically. We need to simulate a torque motor.
>>>>
>>>>
>>>
>>> What's R1 (1G to +5) for?
>> 
>> It can be switched in, and R2 switched out, to make an ohmmeter. Then
>> the opamp is a DC amplifier into an ADC.
>> 
>>>
>>> Are torque motors actually predominantly inductive? Just
>>> because it has coils doesn't necessarily mean it is so.
>> 
>> One case is used in some jet engines, for controlling fuel flow I
>> think. 750 mH and maybe 200 ohms..
>> 
>> Unlike steppers, they seem to have no detent torque and I suspect L
>> doesn't change much with angular position. Gotta machine a test setup
>> and verify that.
>> 
>> If the brushes short windings sometimes, it could get weird.
>
>At first sight, if they're like brushed DC motors, the equivalent
>circuit would be a series combination of an inductor, a resistor
>and a voltage source, function of rotational speed. There will be
>some torque ripple and commutator noise, but there's no telling
>how important that may be.
>
>Jeroen Belleman


https://www.dropbox.com/scl/fo/d9qffkwqzikd9visdt0zi/h?rlkey=mdon4i9xblxkerk470umdbsw3&dl=0


This is charmingly bizarre. There are 41 (prime number!) of commutator
segments. If I pick one arbitrarily, and call it #1, and go clockwise
with an ohmmeter, resistance goes up to about 8 ohms in steps and goes
back down to about 1 ohm at commutator 17, 26, and 34.

This is an NOS motor from ebay. It's an older style with brushes and
alnico magnets.

Imagine designing this 50 years ago without a computer.